#15648: Core Lint error with source-level unboxed equality -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler | Version: 8.4.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #15209 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Replying to [comment:1 goldfire]:
1. Why does GHC type check `Jank` at type `JankyEquality a b`? There must be something in the type checker which treats arguments of type `a ~# b` as invisible. But these shouldn't be -- they are not `Constraint`s. To fix: find this code and kill it.
I think there is a simpler explanation for why this happens: when we kind- check the type `(a ~# b) -> c`, everything works since `(->)` is levity polymorphic and `a ~# b` has kind `TYPE (TupleRep '[])`. This means that resulting `Type` is `FunTy (TyConApp (~#) [TyVarTy a, TyVarTy b]) (TyVarTy c)`—which GHC believes to be `(a ~# b) => c`—so things like `Jank` are seemingly typechecked as if the value of type `a ~# b` were invisible. From a certain perspective, this is a natural consequence of making `a ~# b` have kind `TYPE (TupleRep '[])`. This suggests that one way to work around this issue would be to change its kind. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15648#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler